canard cg
01-21-2004, 08:38 PM
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canard cg
Hello fellow modelers!
I'm attempting to design some .25 size ssc (slow survivable combat) planes.
I've scratch-built many successful planes using the standard configurations, but would like to learn the design parameters needed to build a canard-pusher , namely how to calculate the center of gravity.
Looking at pictures found on the web, it looks like the cg is in front of the leading edge of the main wing.
I've tried a .061 norvel powered home-built ,balanced on the spar, did great loops!! but wouldn't fly...
Any info. would be greatly appreciated!!
THANKs - Greg H.
I'm attempting to design some .25 size ssc (slow survivable combat) planes.
I've scratch-built many successful planes using the standard configurations, but would like to learn the design parameters needed to build a canard-pusher , namely how to calculate the center of gravity.
Looking at pictures found on the web, it looks like the cg is in front of the leading edge of the main wing.
I've tried a .061 norvel powered home-built ,balanced on the spar, did great loops!! but wouldn't fly...
Any info. would be greatly appreciated!!
THANKs - Greg H.
01-21-2004, 08:51 PM
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RE: canard cg
Canard designs have lifting stabilizers in addition to the lifting main wing. This makes you have to play with 3 equations to find the CG instead of just one for a "conventional" aircraft.
first you find 25%MAC for the Canard surface.
Second you find 25%MAC for the main wing.
Now you take Area(canard)X(dist1) = Area(main)X(dist2) where Dist1+dist2 = the distance between MAC line for canard and main wing.
You can be off by 1/2 as much as you can be off on CG for a conventional aircraft. (the 25% MAC is actually a range of 20% to 30% on a canard where its 15% to 33% on a conventional aircraft)
A Canard design should also be set up so the Canard surface ALWAYS stalls before the main wing. (if in doubt balance it a bit noseavy) Canards have a nasty habit of not being able to recover if they get to spinning in reverse. Conventional aircraft just plain won't spin in reverse. (unless the CG is WAY back. Like the 60% MAC CG used on 1930's FF models with lifting tails.)
first you find 25%MAC for the Canard surface.
Second you find 25%MAC for the main wing.
Now you take Area(canard)X(dist1) = Area(main)X(dist2) where Dist1+dist2 = the distance between MAC line for canard and main wing.
You can be off by 1/2 as much as you can be off on CG for a conventional aircraft. (the 25% MAC is actually a range of 20% to 30% on a canard where its 15% to 33% on a conventional aircraft)
A Canard design should also be set up so the Canard surface ALWAYS stalls before the main wing. (if in doubt balance it a bit noseavy) Canards have a nasty habit of not being able to recover if they get to spinning in reverse. Conventional aircraft just plain won't spin in reverse. (unless the CG is WAY back. Like the 60% MAC CG used on 1930's FF models with lifting tails.)
01-21-2004, 09:04 PM
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RE: canard cg
Now you take Area(canard)X(dist1) = Area(main)X(dist2) where Dist1+dist2 = the distance between MAC line for canard and main wing.
Thank you for your reply! but I'm afraid I don't understand "dist1" or "dist2" what are these referring to?
Thank you for your reply! but I'm afraid I don't understand "dist1" or "dist2" what are these referring to?
01-29-2004, 06:14 PM
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RE: canard cg
ORIGINAL: FHHuber
A Canard design should also be set up so the Canard surface ALWAYS stalls before the main wing. (if in doubt balance it a bit noseavy) Canards have a nasty habit of not being able to recover if they get to spinning in reverse. Conventional aircraft just plain won't spin in reverse. (unless the CG is WAY back. Like the 60% MAC CG used on 1930's FF models with lifting tails.)
A Canard design should also be set up so the Canard surface ALWAYS stalls before the main wing. (if in doubt balance it a bit noseavy) Canards have a nasty habit of not being able to recover if they get to spinning in reverse. Conventional aircraft just plain won't spin in reverse. (unless the CG is WAY back. Like the 60% MAC CG used on 1930's FF models with lifting tails.)
Here is a graphical solution
01-29-2004, 06:40 PM
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RE: canard cg
Lets say for example:
Foreplane area = 100 sq in.
Mainplane area = 400 sq in
MAC forplane = 2 in behind LE (at root)
MAC mainplane = 3.5 in behind LE (at root)
Distance between MAC lines is 20 in
dist2 = x, dist1 = y
100 (X) = 400 (y) AND x+y = 20
x = 4y >>>> making substitutions (see HS math teacher)>>> 5x = 20 >>> x = 4
>>> y = 16
******
Note you can always see if you got X and Y backward... the smaller wing is always further from the CG.
The foreplane MAC is 16 inches in front of CG... mainplane MAC is 4 inches behind CG... CG is .5 inches in front of the main wing's LE at root.
Foreplane area = 100 sq in.
Mainplane area = 400 sq in
MAC forplane = 2 in behind LE (at root)
MAC mainplane = 3.5 in behind LE (at root)
Distance between MAC lines is 20 in
dist2 = x, dist1 = y
100 (X) = 400 (y) AND x+y = 20
x = 4y >>>> making substitutions (see HS math teacher)>>> 5x = 20 >>> x = 4
>>> y = 16
******
Note you can always see if you got X and Y backward... the smaller wing is always further from the CG.
The foreplane MAC is 16 inches in front of CG... mainplane MAC is 4 inches behind CG... CG is .5 inches in front of the main wing's LE at root.
